1. Field of the Invention
The present invention relates to motors that are used in industrial equipment and home electric appliances. More particularly, the present invention relates to the structure of motors and motor cases that shorten the overall length of the motors.
2. Description of Related Art
FIGS. 6 and 7 show a typical conventional motor M. The conventional motor M is generally structured with a stator S disposed in a motor case 100 and a rotor R that is freely, rotatably supported within the stator S. The stator S is equipped with a stator core 5 and excitation coils 6. The stator core 5 has a plurality of salient poles disposed at generally equal angles and radially extending toward the center, and each of the excitation coils 6 is wound in generally the same width on each of the salient poles. The stator core 5 is provided with a shaft hole at its center through which a rotary shaft 2 composing the rotor R is passed. The shaft hole is provided opposite to a driving magnet 3 that is affixed to an outer circumference of the rotary shaft 2 of the rotor R.
The rotary shaft 2 is freely, rotatably supported by a pair of bearings 41 and 42 that are provided at both end sides, respectively, of the motor case 100. One end of the rotary shaft 2 outwardly protrudes from the motor case 100 to form an output shaft section 2a. 
The motor case 100 has a cup shape, and is formed from a first case 110 that houses the stator S and a part of the rotor R, and a second case 120 that retains the bearing 42 and covers an opening section of the first case 110. A bearing retaining section 114 is formed in the first case 110 in a manner that the bearing retaining section 114 outwardly protrudes in the axial direction from a bottom surface section 112 of the first case 110. The bearing retaining section 114 retains the first bearing 41 on its inside. Also, a bearing retaining section 124 is similarly formed in the second case 120 in a manner that the bearing retaining section 124 outwardly protrudes in the axial direction from a bottom surface section 122 of the second case 120. The second bearing 42 is retained inside the bearing retaining section 124.
In recent years in particular, the miniaturization of industrial equipment and home electric appliances has been greatly advanced, and in this connection, there is a greater demand in reducing the size of motors themselves. However, since the conventional motor M described above has a structure in which the bearing retaining section 114 protrudes from the bottom surface section 112, which elongates the overall length of the motor M. This prevents miniaturization of the motor M.
Conventionally, some measures to shorten the overall length of motors have been proposed. For example, after the excitation coils 6 are wound on the salient poles of the stator core 5, end faces of the excitation coils 6 are press-formed, or the number of turns of the excitation coils 6 is reduced, to lower the height of the excitation coils 6 in the axial direction.
However, when the end faces of the excitation coils 6 are to be press-formed, additional work is required after the excitation coils 6 are wound, and there is a possibility of severing the excitation coils 6. When the number of turns of the excitation coils 6 is reduced, there may be a problem in that the designed motor performance may not be attained.
The present invention has been made in view of the problems described above. Accordingly, the present invention relates to providing motors that can realize miniaturization of motors by shortening the overall length of the motors.
In accordance with an embodiment of the present invention, a motor includes a case body having a bottom surface section, a recessed concave section that is located inside the bottom surface section in a radial direction and recedes inwardly in an axial direction at a location opposite to an excitation coil provided within the case body, and a bearing retaining section that is formed inside the recessed concave section in the radial direction, wherein at least one part of the bearing retaining section is located inside in the axial direction than the bottom surface section.
In accordance with the present invention, the bearing retaining section is disposed inside the recessed concave section in the radial direction that is located opposite to the excitation coil and inside the bottom surface section of the case body the radial direction of. As a result, the bearing can be located more interior in the axial direction than the bottom surface section. Consequently, the amount of protrusion of the bearing retaining section that may protrude from the bottom surface section of the case body is suppressed to a small level, and thus the overall length of the motor can be shortened.
Also, in the present invention, the excitation coil may be wound in a manner that the number of turns of the excitation coil becomes greater toward outside in the radial direction such that an end face of the excitation coil is inclined inwardly in the axial direction, and the recessed concave section may have a sloped surface section that is concaved inwardly in the axial direction and extends along the inclined end face of the excitation coil.
In one embodiment, each of the salient poles of the stator core may be formed from a base section that is located on the outer circumferential side of the stator core, an extended section that is to be located opposite to the driving magnet on the inner circumferential side of the stator core and a rib section that connects the base section and the extended section. The width of the base section may be wider in the circumferential direction than the width of the extended section. By using such a structure of the stator core, the configuration of excitation coil whose number of turns becomes greater in the radial direction toward the outer periphery of the stator core can be more rationally achieved.
With the structure described above, the excitation coil can be wound on the salient pole of the stator core in the amount necessary to provide its intended function without creating waste spaces in the circumferential direction, and the end face of the excitation coils become inclined in the axial direction. As a result, the recessed concave section of the case body can be inwardly concaved along the inclined end faces of the excitation coils, and spaces along the axial direction of the case body can be effectively utilized to reduce the amount of protrusion of the bearing retaining section. As a consequence, while the necessary number of turns for the excitation coil is maintained, the overall length of the motor can be shortened.
In accordance with an embodiment of the present invention, the stator core may be divided in the circumferential direction for each of the salient poles; in other words, the stator core may be formed from a plurality of divided cores that are circularly arranged in a ring shape. The excitation coil may be wound on each of the divided cores. By so doing, the coil winding work on each of the salient poles becomes simpler, and a motor with good volume efficiency as a whole and high occupancy rate of the excitation coils can be structured.
Furthermore, in accordance with an embodiment of the present invention, the case body may have two sides that interpose the stator core in the axial direction, and each of the sides may have the bottom surface section, the recessed concave section and the bearing retaining section, and each of the bearing retaining sections may retain a bearing, wherein at least a part of each of the bearings may be located more interior in the axial direction than the bottom surface section.
With the structure of described above, at least a part of each of the bearings retained at both of the two sides in the axial direction of the case body is located more inside in the axial direction than the bottom surface sections. As a result, the overall length of the motor can be further shortened.
In accordance with another embodiment of the present invention, a motor includes a case body containing a rotor core, wherein the case body includes a bottom surface section that closes an opening section of the case body, a recessed concave section that is located radially inside the bottom surface section and recedes inwardly in an axial direction at a location opposite to an excitation coil provided within the case body, and a bearing retaining section that is formed radially inside the recessed concave section, wherein at least one part of the recessed concave section is located more interior in the axial direction than the excitation coil.
In accordance with the embodiment described above, the recessed concave section that is formed opposite to the excitation coil is provided inside in the radial direction of the bottom surface section, and the bearing retaining section is disposed inside in the radial direction of the recessed concave section. As a result, the amount of protrusion of the bearing retaining section that may protrude from the bottom surface section of the case body is reduced to a small level, and thus the overall length of the motor can be shortened.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.